Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

199
FXUS63 KLOT 091142
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
642 AM CDT Thu Jul 9 2026

.KEY MESSAGES...

- Scattered thunderstorms are expected at times through this
  evening. These storms will be capable of locally heavy
  rainfall which may lead to flooding, particularly if they
  stall or redevelop over areas hardest hit from last weekend.

- The strongest storms will also be capable of gusty to locally
  damaging wind gusts this afternoon and evening, greatest
  threat south of I-80.

- Mainly dry and warmer weather is expected this weekend into
  early next week.

&&

.DISCUSSION...
Issued at 342 AM CDT Thu Jul 9 2026

The earlier complex of thunderstorms approaching from eastern
IA/southwest WI has mostly eroded with only a few areas of rain
remaining. Not currently expecting any additional lightning
through the remainder of the overnight hours with this activity
but will still have to keep an eye on the remnant MCV moving
into northwest Illinois but it should move out over the lake
already by 7-8 AM. Earlier warm advective showers southwest of
the metro managed to produce a few lightning strikes but have
since decreased in coverage. Still can`t rule out a few spotty
showers south of the Kankakee River Valley through daybreak.

Attention then turns to a second MCV moving across central
Iowa. This feature is expected to progress east toward the area
through mid morning. Concerns are that this could lead to an
earlier "first round" of isolated to scattered showers and
thunderstorm development from mid morning through early
afternoon (30-40 percent chance). Forecast soundings show a
largely uncapped environment here locally already after 9-10 AM
so any forcing for ascent (such as with an MCV) would support
thunderstorm development. Model guidance has been struggling
with handling these smaller scale mesoscale features and have
based the first 12 hours of the forecast largely on radar,
satellite, and observational trends.

As the aforementioned MCV begins to shift southeast out of the
area toward mid-late afternoon, additional thunderstorm
development may then occur within the vicinity of a residual
outflow boundary or convergence axis situated across northern
and northeast Illinois. Exactly where this boundary ends up as
well as what the coverage of showers/storms will be remains
lower confidence, at least initially given a potentially slower
arrival of the parent mid-level vort/wave (which is still out
over northern NE/southern SD). Suspect that coverage may remain
more isolated to widely scattered during the afternoon until the
wave arrives leading to increasing coverage during the evening
(potentially still over portions of the Chicago metro) before
gradually shifting south and east and out of the area overnight.

The primary hazard with any thunderstorms today (from mid
morning through this evening) will be localized heavy rainfall.
PWATs in the upper end of climatology (2"+) will be supportive
of instantaneous rainfall rates in excess of 1-2"/hr. Given the
increased susceptibility for flooding in many areas after last
weekend`s multiple rounds of heavy rainfall, will continue to
message the localized threat of flooding. In spite of generally
weaker shear, precip loaded downbursts will remain possible with
the strongest storms which could produce strong to locally
damaging wind gusts (40-60 mph). The greatest threat (and level
1 out of 5 threat for severe weather) is greatest for areas
well south of I-80 but can`t fully rule it out areawide.

In the wake of our showers and storms a backdoor cold front is
expected to move inland off Lake Michigan late in the evening.
This may bring a period of fog and/or very low clouds across
much of the metro through early Friday morning, some of which
could end up locally dense. Something to keep an eye on with
later forecasts.

Looking ahead to Friday, additional convectively augmented
shortwaves are expected to move across the Mid-Mississippi and
Ohio Valley regions. Think that the majority of the shower and
storm coverage with these features will remain largely south of
the area but have maintained 20-40% chances for areas south of
a Peru, IL to Rensselaer, IN line in case they end up a bit
farther north.

While a few diurnally driven showers can`t be ruled out on
Saturday, upper level ridging expands across the central CONUS
over the weekend into early next week which should lead to
mainly dry conditions into the first part of next week with
temperatures in the upper 80s to around 90. Given we will be on
the northeast periphery of the ridge we will have to monitor the
potential for thunderstorm complexes rounding the ridge across
the broader region toward midweek.

Petr

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 642 AM CDT Thu Jul 9 2026

Forecast concerns for the terminals...

- 20-30% chance for isolated to widely scattered showers and
  perhaps an isolated storm this morning.

- Scattered showers and thunderstorms expected this afternoon
  and evening which will be capable of locally heavy rainfall
  resulting in reduced visibilities.

- MVFR ceilings to develop late this evening and linger through
  Friday morning. Fog is also possible after midnight and could
  become locally dense especially near Lake Michigan.


A convectively enhanced low pressure center is drifting across
eastern IA this morning and has started to develop some isolated
showers along its eastern periphery. This feature is expected
to continue eastward across northern IL and eventually into
northwest IN through midday and may continue to produce isolated
to widely scattered shower and perhaps even a thunderstorm
(15-20% chance of a storm) as it does so. While the environment
is supportive of showers/storms, this forecast is lower
confidence since coverage of showers/storms will be more hit and
miss. That said, opted to introduce PROB30s for SHRA into the
TAFs for a couple hours this morning to account for this
potential.

Heading into this afternoon, any morning showers/storms will
exit the area and likely give us a 1-3 hour break in the weather
before additional showers and storms start to develop along an
outflow boundary that is forecast to be draped over northeast
IL. The afternoon shower/storms should be of a higher coverage,
but timing as to when exactly things will initiate makes this
forecast too a bit lower confidence. Despite the low to medium
confidence in timing, have introduced VCTS starting in the early
afternoon through mid-evening to account for the uncertainty in
timing with more targeted TEMPOs for the 3-4 hours confidence
is highest in storms occurring at each terminal. Given the humid
air mass in place, storms today will be capable of locally
heavy rainfall which will lead to reduced visibilities in the
IFR range. There is also the potential for locally gusty winds
in the strongest storms where gusts in excess of 30-40 kts could
occur.

Showers and thunderstorms should gradually push south and east
of the terminals through the evening with most sites starting to
dry out around 03z. However, there is some indication that some
showers could linger through midnight (or even later). Behind
the shower/storms, ceilings will lower to MVFR where they are
expected to remain through the rest of the TAF period. In fact
some IFR ceilings cannot be ruled out especially near Lake
Michigan. Additionally, fog is forecast to develop over the lake
this evening and ooze inland overnight some of which may become
locally dense. With the uncertainty in how late showers/storms
will linger, confidence is lower on how dense fog will become so
have opted to keep 6SM BR going in the TAFs for now. Any fog
that does develop tonight will erode shortly after daybreak on
Friday.

Finally, winds today will generally be out of the west-southwest
with speeds around 10 kts but directions will likely be variable
in and around thunderstorms. Winds will become northeasterly
this evening as the aforementioned outflow moves through and
will remain northeast through the rest of the period with
lighter speeds around 5-7 kts.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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